1. Field of the Invention
The present invention relates to a common rail type fuel injection system for supplying pressurized fuel into an internal combustion engine such as a diesel engine.
2. Description of Related Art
An example of this type of a fuel injection system is disclosed in JP-A-2001-295685. In this system, fuel in a fuel tank is sucked by a feed pump and fed to a fuel supply pump that pressurizes the fuel. The pressurized fuel is supplied to a common rail that accumulates therein the pressurized fuel. The pressurized fuel is injected from an injector into a cylinder of a diesel engine. Injection timing and amount of fuel injected into the cylinder are controlled by an electronic control unit.
There has been the following problem in such a conventional system. An amount of fuel sucked by the feed pump is small when the engine is under an idling state and at a low load. Accordingly, a flow speed of the fuel is low, and air in the fuel tank sucked together with the fuel is gradually accumulated in a fuel filter connected between the fuel tank and the feed pump. After a certain amount of the air is retained in the filter, the retained air is sucked at a time into the feed pump. When a large amount of air is sucked at a time into the feed pump, fuel to be supplied to the common rail cannot be sucked by the feed pump. Therefore, fuel pressure in the common rail drops, and fuel supply to the engine is temporarily discontinued. If this happens, the engine will come to a stall.